Chronic hypoxia (CH) associated with obstructive pulmonary disease and sleep apnea often results in generalized pulmonary arterial constriction and vascular remodeling, subsequent pulmonary hypertension and right heart failure. Pulmonary arterial smooth muscle cell (PASMC) intracellular calcium ([Ca2+]i) plays a vital role in establishing pulmonary vascular resistance and it has become increasingly evident that increased Ca2+ influx contributes to both the vasoconstrictor and vascular remodeling responses in CH-induced pulmonary hypertension. Our laboratory has found a novel role for acid sensing ion channel 1 (ASIC1) in mediating store-operated Ca2+ entry (SOCE) in PASMC following CH. However, little is known about the mechanism(s) that govern ASIC1 trafficking, stability, and activation in PASMC. In addition, it is unclear how CH alters these mechanism(s) to increase functional ASIC1 at the plasma membrane. The overall objective of this application is to establish an important role for ASIC1 in the development of CH-induced pulmonary hypertension and potential mechanisms involved in this response. We will test the central hypothesis that ASIC1, through a novel mechanism of SOCE in PASMC, contributes to CH-induced increases in vascular reactivity and pulmonary hypertension with the following specific aims: 1) Determine the contribution of ASIC1 to CH-induced pulmonary hypertension. We will test the hypothesis that ASIC1 contributes to the active vasoconstrictor component of CH-induced pulmonary hypertension by assessing in vivo measurements of pulmonary arterial pressure, arterial remodeling, and vasoreactivity. 2) Identify the mechanism(s) responsible for ASIC1 membrane trafficking and how this is altered by CH. We will test the hypothesis that CH promotes PICK1 (protein interacting with C- kinase 1)-dependent ASIC1 trafficking to the membrane through increased RhoA-mediated actin polymerization by use of cell surface biotinylation assays, [Ca2+]i imaging, and live-cell confocal imaging of a fluorescently- labeled ASIC1 protein. 3) Examine the effect of cellular redox potential on ASIC1 activation. We hypothesize that decreased hydrogen peroxide (H2O2) following CH increases ASIC1 surface expression and channel activity. We will assess vasoreactivity and conduct [Ca2+]i imaging and electrophysiology studies to examine the role of reducing/oxidizing agents and H2O2 on ASIC1 channel activity and trafficking in PASMC. The proposed research is innovative through its focus on the previously undefined mechanisms of ASIC1 membrane trafficking, channel regulation and Ca2+ influx in the normal pulmonary circulation. In addition, our work is at the forefront of determining how hypoxia affects ASIC1 function in the hypertensive circulation. Successful completion of the proposed research will provide a mechanistic-based understanding of how ASIC1 contributes to CH- induced pulmonary hypertension and will significantly advance our knowledge of the cellular mechanisms responsible for altered PASMC Ca2+ homeostasis and vasoconstriction in the hypertensive pulmonary circulation. Ultimately, such knowledge has the potential to provide new directions in pulmonary hypertension therapy.